Distillation process



y 1943- J. R. SCHONBERG, EI'AL 2,319,750

DISTILLATION PROCESS Filed Aug. 12, 1939 C ON-DENSE FLASH ZONE STEAM-457- .S TR P NC ZONE Wigwam Patented May 18, 1943 DISTILLATION PROCESSJackson R. Schonberg and James B. Maxwell,

Westfield, N. J., assignors to Standard Oil Development Company, acorporation of Delaware Application August 12, 1939, Serial No. 289,762

6 Claims.

boiling range and for the production of low penetration asphalts. Inaccordance with the present process, a small portion of the oil from' aplate above the flash zone is withdrawn and recirculated with the freshfeed through the heating coil while the temperature of the oil in thestripping section is maintained substantially equivalent to or above thetemperature of the entering feed to the flash zone by removing oil fromthe stripping section, reheating and returning the same.

Recirculation of relatively high boiling stock with the fresh feed isknown in flash distillation operations. However, the recirculated highboiling stock is usually withdrawn from the distillation tower at apoint below the point of introduction of fresh feed. These recirculationoperations are conducted primarily to effect a better flash distillationoperation by preventing an excessive drop in temperature of theunvaporized portions from the flash zone. An excessive temperature dropis undesirable below the flash zone since further vaporization of theoil is materially decreased-and relatively large quantities of steam arenecessary in order to vaporize the desired amount of the oil from theliquid bottoms. Thus, the added portion of high boiling oil recirculatedthrough the furnace or heating coil with the fresh feed and to the flashzone serves as an added heat reservoir from which sensible heat may besecured to supply suflicient latent heat in order to effect the desiredvaporization without causing an excessive temperature drop of theunvaporized oil.

In operations of this character it is necessary to recirculate arelatively large amount of oil in order to supply an ample reservoir ofsensible heat so that an excessive temperature drop will not occur dueto the amount of latent heat removed in securing the desiredvaporization. Re-

circulation of a large volume of oil is not desirable since it dilutesthe oil which is to be flashed with relatively high boiling fractionsand thus offsets, to a large extent,.the benefits of preventing asubstantial temperature drop in the flash zone. Recirculation of arelatively large volume of oil is also undesirable in that increasinglylarger equipment is needed in order to secure the desired capacity.

It is also known in flash distillation operations to remove oilfractions not vaporized in the flash zone by means of open steam in astripping section. In these operations it has been found that thevaporization of the fractions to be removed occurs principally on theupper plates of the stripping section. The latent heat of vaporizationrequired on these plates to secure the desired vaporization materiallylowers the temperatures. This is undesirable since steam stripping onthe plates below the flash zone becomes increasingly less'efiective asthe temperatures of the respective'plates are lowered.

We have now discovered a process by which it is possible to secure anoptimum separation between the overhead products and the bottoms productin a distillation operation and to effect material economies in thedistillation of oils. In accordance with our process, a relatively smallamount of oil' is withdrawn from a plate above the flash zone andrecirculated through the heating coil with the fresh feed andreintroduced into the flash zone, while the temperature in the strippingsection is maintained substantially equivalent to or above thetemperature of the entering feed to the flash zone by simultaneouslywithdrawing oil from the stripping section, reheating and returning theoil to the stripping section. We have discovered that when thedistillation operation is conducted in this manner it is possible tosecure high yields of high vi..- cosity lube fractions boiling in therange immediately above the asphalt boiling range and to simultaneouslyproduce low penetration asphalt/s as determined by the A. S. T. M. test.

- Our process may be readily understood by ref erence to the attacheddrawing illustrating one modification of the same. Fresh feed oil isintroduced into furnace l by means of feed line 2. This oil flowsthrough the radiant and convection sections of furnace l and iswithdrawn by means of line 3 and introduced into flash zone 4 ofdistillation tower 5. Steam may be introduced into the feed oil infurnace l by means of steam line 6. Temperature and pressure conditionsare maintained in distillation tower 5 adapted to secure a flashoperation and to remove overhead the desired amount of the fresh feedwithout causing appreciable decomposition of, the same. The vaporizedportions of the oil flashed in flash zone 4 pass upwardly through afractionating section I of distillation tower 5. Section I contains asuitable number of bubble cap plates or their equivalent. Theunvaporized portions of the oil pass downwardly from flash zone 4 intostripping zone 8. Stripping section 8 contains a suitable number ofbubble cap trays or their equivalent. Steam is introduced below thestripping zone by means of line IS in order to assist in the removal ofthe desired amount of vapors from the unvaporized oil. Heavy unvaporizedbottoms are withdrawn from distillation tower by means of line 9. A sidestream of intermediate boiling range may be withdrawn from distillationtower 5 by means of line Ill. The overhead vaporized portion iswithdrawn from distillation tower 5 by means of line H, condensed incondenser I2, and passed to distillate drum [3. Reflux is returned totower 5 by means of line H. Uncondensed vapors are removed fromdistillate drum I3 by means of line 20, while the condensed distillateproduct is removed by means of line 2!. An oil cut is withdrawn from theplate in the fractionating section immediately above the flash zone bymeans of line l5, recirculated with the fresh feed through furnace Iinto flash zone 4. Another oil cut is simultaneously withdrawn from aplate in the stripping section below the upper plate by means of lineI6, reheated in a separate coil in coil furnace l and then reintroducedinto the stripping section on the plate from which it was withdrawn oron a plate immediately below the point of withdrawal by means of linesI! and 22. Steam may be introduced into the oil being reheated by meansof line l8.

The process of the present invention may be widely varied. The inventionis readily applicable in the distillation of any oil and is especiallydesirable in the flash distillation of oils boiling in the range aboveabout 550 F. In accordance with the preferred modification of thepresent invention, conditions are adapted in the distillation operationto remove overhead from 50% to 95% of the fresh feed. In general, it ispreferred to recirculate with the fresh feed a relatively small criticalquantity of oil which includes the highest boiling fractions of theoverhead products and the lowest boiling fractions of the bottomsproducts, The quantity of oil recirculated with the fresh feed shouldpreferably be below i 10% and not over based upon the total quantity offresh feed.

It is quite important that the relatively small quantity of recirculatedoil should contain the relatively low boiling constituents of thebottoms and the relatively high boiling constituents of the overhead andthat the temperature of the stripping section be maintained bywithdrawing, reheating, and returning relatively higher boilingfractions from the stripping section. The amount of oil withdrawn,reheated and returned to the stripping section will be adjusted tomaintain the temperature in the stripping section substantiallyequivalent to or above the temperature of the entering feed to the flashzone. In certain operations a reheating operation may be desirable, inwhich case the entire quantity of oil is withdrawn from an upper plate,preferably from the first or second plate adjacent the flash zone,reheated and returned to a plate immediately below the plate from whichit was withdrawn. In other operations it is desirable to recirculate aquantity of oil which may be either greater or less than the quantity ofoil flowing down the stripping section. If the latter opera- Theseresults are secured since the removal and recirculation with the freshfeed of a relatively small portion of oil from the flash sectionenhances the efliciency of the stripping section, while the reheating ofthe oil in the stripping section substantially improves the efiectivevalue and results secured by recirculating the oil with the fresh feed.

The present invention is not to be limited in any manner whatsoever, butonly in and by the following claims in which it is desired to claim allnovelty insofar as the prior art permits.

We claim:

1. Process for the flash distillation of oil for the production ofmaximum yields of high viscosity oils boiling immediately above theasphalt boiling range and for the production of low penetration asphaltscomprising heating a feed oil by passing the same through a heatingcoil, withdrawing and introducing the heatedfeed oil into a distillationtower under conditions to secure flash vaporization of a substantialamount of the oil, passing vaporized portions upwardly through the towerinto a fractionating section, withdrawing a portion of the oil from aplate in the fractionating section immediately above the flash zone andrecirculating the same in the absence of added recycled higher boilingoils through said heating coil into the flash zone with the fresh feed,passing unvaporized portions of the oil downwardly from the flash zoneinto a stripping section, withdrawing oil from an upper plate in saidstripping section, reheating and returning the same to a plate in saidstripping section under conditions adapted to secure in said strippingsection a temperature at least substantially as high as the temperatureof the entering feed into said flash zone.

2. Process in accordance with claim 1 in which said oil withdrawn andreturned to said stripping section is reheated under conditions adaptedto secure in said stripping section a higher temperature than thetemperature of the fresh feed entering into said flash zone.

3. Process in accordance with claim 1 in which conditions of saiddistillation tower are adapted to secure 50% to flash vaporization ofthe feed oil in said flash zone and stripping section.

4. Process for the flash distillation of oils for the production ofmaximum yields of high viscosity oils boiling immediately above theasphalt boiling range and for the production of low penetration asphaltscomprising heating a petroleum oil by passing the same through a heatingzone, introducing said oil into a flash zone of a distillation towerunder conditions to secure substantial vaporization of the oil, passingvaporized portions of the oil upwardly through a fractionating section,withdrawing from a plate immediately above said flash zone an oilcontaining relatively low boiling constituents of the bottoms andrelatively high boiling constituents of the the amount of saidrecirculated oil is less than 10%, based upon the fresh feed.

6. Process in accordance with claim 4 in which the temperature in saidstripping section is maintained at least equivalent to the temperatureof the fresh feed oil by withdrawing the oil from the plate immediatelybelow the flash zone, re-

heating the same, and returning the withdrawn oil to the same plate.

JACKSON R. SCHONBERG. JAMES B. MAXWELL.

